(1) Field of the Invention
This invention relates a substrate treating apparatus for drying substrates such as semiconductor wafers or glass substrates for liquid crystal displays (hereinafter called simply substrates). More particularly, the invention relates to a technique for drying substrates by moving the substrates out of a treating liquid into a solvent atmosphere while a chamber of the solvent atmosphere is decompressed.
(2) Description of the Related Art
A conventional apparatus of this type includes a treating tank for storing deionized water, a chamber enclosing the treating tank, a holding mechanism for vertically moving substrates between a treating position inside the treating tank and a drying position above the treating tank, nozzles for supplying a vapor of isopropyl alcohol (IPA) into the chamber, a vacuum pump for decompressing the chamber, and a drain pipe for discharging the deionized water from the treating tank to the exterior of the chamber (see Japanese Unexamined Patent Publication H11-87302 (1999), for example).
In the apparatus of such construction, a lift arm is first moved to the treating position to have substrates cleaned with deionized water. Then, a vapor of isopropyl alcohol is supplied from the nozzles to fill the chamber with a solvent atmosphere. Subsequently, the holding mechanism is moved to the drying position. Next, the vacuum pump is operated to decompress the chamber, and the isopropyl alcohol adhering to the substrates is dried to dry the substrates.
The conventional apparatus with the above construction has the following drawbacks.
In the conventional apparatus, deionized water stored in the treating tank inside the decompressed chamber could have an adverse influence on drying treatment of the substrates. It is therefore necessary to discharge the deionized water from the treating tank in the state of atmospheric pressure before decompressing the chamber. That is, since the water cannot be drained during decompression of the chamber, there is a problem of low throughput of substrate treatment from treatment with the treating liquid to drying treatment.
In order to avoid the above inconvenience, it is conceivable to discharge deionized water from the treating tank while pressurizing the inside of the chamber with an inert gas such as nitrogen, for example, after forming a solvent atmosphere and decompressing the chamber. However, such pressurization condenses the vapor of isopropyl alcohol in the chamber, whereby isopropyl alcohol adheres to the substrates as droplets producing a residue thereon. This poses a different problem that the substrates cannot be dried clean.